In many types of industrial dewatering systems mediums such as papermaker's felts, require dewatering periodically during use. For this purpose, a variety of different types of suction dewatering systems have been developed including those which employ suction boxes or suction pipes. The pipes or boxes include a slot structure with an upper wear surface over which the medium such as a felt passes into alignment with a slot subjected to a source of suction. Water is drawn by the suction force from the felt as it passes over the slot and is collected in the box or pipe and then is disposed of in a conventional manner.
In use, as the felt or similar material ages it undergoes a physical change whereby parameters such as permeability are changed. A decrease in permeability, for example, causes a greater resistance to dewatering with increased age of the medium. Thus, the dewatering system requires modification as the felt ages in order to maintain an acceptable efficiency in the dewatering procedure. A number of different criteria are used to keep the dewatering process at acceptable efficiency level. One acceptable way of achieving the desired dewatering result as the felt ages is to increase the slot width. This provides for greater exposure of the felt to the suction force as it passes over the slot as well as increasing the dwell time of the felt over the slot and accordingly the time during which it is subjected to the vacuum and water is removed.
Presently known systems employ various acceptable manual procedures for changing slot width such as the system disclosed in U.S. Pat. No. 3,836,428. In this type of system, the manual changing of the slot size is achieved by changing the shape and configuration and sizes of portions of the slot cover. This system works effectively for the purposes discussed above, however, it does result in an interruption in the dewatering process. Naturally in a manual system, the changing process causes the dewatering rate to drop off until the slot opening is manually changed. Of course during the actual changing time the machine is not operating at all and accordingly no dewatering is taking place.
Therefore, further improvements in suction dewatering systems are desirable particularly a system which will automatically adjust the slot size as the felt or similar medium ages without requiring the felt to be periodically checked to determine if it is operating efficiently and without the need of shutting down the machine to manually adjust slot sizes by changing slot cover configurations.
It should also be kept in mind that the manually adjustable systems require an abrupt change in slot size rather than a gradually changing automatic adjustment. Any type of manual system that would utilize gradual change would require frequent manual slot adjustments causing frequent interruption in the use of the machinery.